Guidewires for use in, for example, percutaneous transluminal coronary artery angioplasty (PTCA), must be thin and flexible enough to advance through small arteries toward the coronary artery. These wires must also be sturdy enough to be manipulated from the outside of the body, such that a distal end of the wire can be brought into contact with a selected region of the coronary artery. Further, they must be strong enough to survive a "pull test" without breaking, to ensure that they do not come apart in the body.
Prior known guidewires each essentially include a solid tapered core and an elongated non-radiopaque coil or sleeve that is coincident with and extends over a distal portion of the core. The coil or sleeve adds strength to the tapered distal end of the core, essentially without limiting its flexibility. Each of the guidewires also has a radiopaque distal end that is 1 to 3 centimeters in length. This allows the cardiologist to observe, using x-ray or fluoroscopy, the progress of the wire through the arteries. The remainder of the wire is non-radiopaque, to avoid obscuring the arteries from view.
These guidewires differ in how the radiopaque distal ends are formed, and there are essentially two types of guidewires.
One type of prior known guidewire includes a shorter radiopaque end coil that is attached to the distal end of an elongated non-radiopaque coil. The two coils have the same outer diameter and are typically made from coil wires that have the same thickness. The elongated coil is made from a material, such as stainless steel, which is relatively inexpensive. The shorter radiopaque coil is made from a precious metal, such as platinum, and is thus relatively expensive, even though it is fairly short.
A problem with this guidewire, beyond the expense of the radiopaque coil, is that it is difficult to assemble. The distal end of the elongated coil and the proximal end of the shorter coil must be held completely flush while they are welded or soldered together, to ensure a strong joint. Since these coils are each approximately 0.014 inch in diameter, it is difficult to hold them in proper alignment during the welding or soldering operation. There is also a danger that the two coils may become unattached during use. If this happens, the radiopaque coil may slide off the end of the essentially smooth core and become free in a patient's body.
Another type of prior known guidewire has at its distal end a radiopaque coil that is positioned inside the distal end of the elongated coil. This arrangement essentially prevents the radiopaque coil from sliding off the core, since the elongated coil provides a rough surface that frictionally holds the shorter coil in place. Further, this guidewire is relatively easy to assemble, since the elongated coil holds the shorter coil in place for soldering or welding once the coil is positioned within the distal end of the elongated coil.
The radiopaque coil used in the latter guidewire must be made quite small, to fit within the distal end of the elongated coil. The elongated outer coil typically has an outer diameter of approximately 0.014 inch and an inner diameter of 0.011 inch or less. Accordingly, the outer diameter of the inner radiopaque coil must be 0.010 inch or less to fit within the elongated coil. A problem with a radiopaque coil that has such a small outer diameter is that the coil is difficult to discern under x-ray or fluoroscopy. This guidewire may thus be difficult to use.